sedimentary

Petoskey Stone

Hexagonaria percarinata (Fossilized colonial coral)

AI-generated identification · may be incorrect

Hardness: 3.0-3.5 on Mohs scale; Color: Gray to brown, appearing uniform when dry and revealing a distinctive hexagonal pattern when wet; Luster: Dull to sub-vitreous; Structure: Hexagonal colonial skeletal structure; Specific gravity: Approx 2.7.

Hardness: 3
Luster: Dull to sub-vitreous

Identified April 10, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed during the Devonian Period (approx. 350 million years ago) from colonial corals that lived in warm, shallow seas. As mountains rose, the sea receded, and the coral beds were buried and fossilized into limestone. Later, glacial action during the Pleistocene epoch plucked them from their bedrock and deposited them across Michigan.

Uses & applications

Used primarily in jewelry (beads, pendants), as decorative items, souvenirs, and highly prized by fossil collectors and lapidary enthusiasts.

Geological facts

It is the official state stone of Michigan. The name comes from an Ottawa Chief, Pet-O-Sega, which means 'Rising Sun' or 'Rays of Hope' because the pattern resembles a sun.

Field identification & locations

Identify by wetting the stone to reveal the six-sided 'honeycomb' pattern. They are most commonly found on the shores of Lake Michigan and Lake Huron, particularly in the Petoskey and Charlevoix areas of Michigan.